are the 4x4 rear diffs different from the 2wds??? i know the casings are ie 7inch-4x4 7.5inch-2wd and the driveshaft hubs but are the ratios? and if they are which 1 would be good for acceloration?

 

Have a look here, it can help you a bit
https://passionford.com/forum/general-car-related-discussion/247724-cosworth-4x4.html

 

yes they are different, but only slightly 3.64:1 vs 3.62:1 this equates to about the same as new tyres vs worn tyres in speed difference, I would not recommend changing. the rwd uses the bigger 7.5" diff because it is stronger and all the power is transmitted through the rear this is why the shafts are also bigger, the 4x4 shares the power through both diffs and therefore doesnt need the bigger diff and shafts. if your car is 4x4 and you fit the 7.5" diff then the front and rear props will turn at different speeds which will overwork the centre diff. to summarise leave as is and replace like for like!